Heidemann S R, Kirschner M W
J Exp Zool. 1978 Jun;204(3):431-44. doi: 10.1002/jez.1402040314.
We have previously reported that injection of purified basal bodies or sperm into unfertilized eggs of Xenopus laevis induced the formation of asters and irregular cleavage furrows. Fully grown oocytes were found to be unable to form asters or cleavage furrows. In this paper we show that the oocyte acquires the ability to form asters upon basal body injection at the time of germinal vesicle breakdown during in vitro maturation. Our evidence indicates that aster formation requires progesterone-stimulated changes in the oocyte and mixing of cytoplasm and germinal vesicle plasm. The ability of the oocyte to form cleavage furrows arises six to eight hours after germinal vesicle breakdown. We infer that some maturational change in the cell cortex occurs to enable the egg surface to furrow. Experiments on the relationship of aster formation to furrow initiation indicates that asters stimulate furrow formation. However, some furrowing could be induced without aster formation in mature oocytes and unfertilized eggs by an activation stimulus, showing that asters are not essential for cleavage initiation. The significance of these observations are discussed in the light of our current understanding of meiotic maturation, cell cleavage and aster growth.
我们之前曾报道，将纯化的基体或精子注入非洲爪蟾未受精卵中会诱导星体和不规则分裂沟的形成。研究发现，完全成熟的卵母细胞无法形成星体或分裂沟。在本文中，我们表明卵母细胞在体外成熟过程中，在生发泡破裂时注入基体后获得了形成星体的能力。我们的证据表明，星体形成需要孕酮刺激卵母细胞发生变化以及细胞质与生发泡细胞质的混合。卵母细胞形成分裂沟的能力在生发泡破裂后六至八小时出现。我们推断，细胞皮层发生了一些成熟变化，使卵表面能够形成沟。关于星体形成与沟起始关系的实验表明，星体刺激沟的形成。然而，通过激活刺激，在成熟卵母细胞和未受精卵中，即使没有星体形成也能诱导一些沟的形成，这表明星体对于分裂起始并非必不可少。我们根据目前对减数分裂成熟、细胞分裂和星体生长的理解，讨论了这些观察结果的意义。
